Does multiverse really explain fine-tuning?

In summary, the conversation discusses the concept of the multiverse and its potential role in solving the problem of fine-tuning in our universe. The question is raised of whether there still needs to be a "multiverse generator" that is fine-tuned for creating different universes. It is noted that this is not a new issue and is known as the "measure problem." The conversation also touches on the idea of the Anthropic Principle and the debate over whether fine-tuning is a religious statement or a necessary aspect of our observations. Overall, the conversation acknowledges that the multiverse theory may push the problem of fine-tuning one step further, but it still offers a possible explanation for the observed physical constants.
  • #1
abc5
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0
Hello everyone,

I am not sure about this issue and this is the reason why I am asking this question. I can write many sentences on this topic, but I will try to make my point as short is possible.

I will suppose you are familiar with multiverse idea and anthropic principle..

My question is: Let's suppose there are billions and billions of other universes, does that solve problem of fine-tuning? Wouldn't there still have to be some fundamental laws which creates universes in multiverse- in other words, wouldn't there have to be "multiverse generator" which would have to be fine-tuned "for creating other universes with different constants"... Am I missing something, or with multiverse theory problem is not solved, just pushed one step further?
 
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  • #2
abc5 said:
Wouldn't there still have to be some fundamental laws which creates universes in multiverse- in other words, wouldn't there have to be "multiverse generator" which would have to be fine-tuned "for creating other universes with different constants"
There is no fine-tuning involved in this part, because the creation of universes can be very general. You don't need to be a good darts player to hit random spots on the wall with each attempt, but you have to be good to hit the bullseye with one attempt.
 
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  • #4
But you still need a mechanism which would throw the arrows... If I get this right, the mechanism is eternal inflation, which will produce the universes forever-infinite number of universes..

But what if there is no infinite number of universes? What if there is no such thing as eternal inflation, and at one point, inflation have to stop... Let's suppose there is finite number of universes, and if there is no enough universes to cover "fine-tuning of our universe" then the multiverse theory, would not solve the problem of fine-tuning.. Is that correct?
I am not challenging anything or anybody, as you can see, english is not my native language( I am sorry for my grammar mistakes) and I am not physicist... But there are some ideas, which would make eternal inflation impossible, so because of that I am asking the question...
https://www.newscientist.com/article/mg22229692-600-quantum-twist-could-kill-off-the-multiverse/
 
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  • #5
The Anthropic Principle seems neater.fine-tuning is a semi-religious statement. We are a product of the universe, so we should not be suprised that the universe looks the way it does.
 
  • #6
William White said:
fine-tuning is a semi-religious statement. We are a product of the universe, so we should not be suprised that the universe looks the way it does.

But it is a good religion. Its philosophy is that all our theories are wrong, and not the final theory. If we knew the true final theory, then we wouldn't be surprised if it is fine tuned, since the true ultimate reality is simply what it is.

One technical way of stating this religion is via Wilsonian renormalization.
 
  • #7
A number of posts have been deleted, please keep to the original topic given by the OP about fine tuning and the multiverse.
 
  • #8
abc5 said:
But you still need a mechanism which would throw the arrows
Right, but this mechanism does not have to be fine-tuned. It just has to exist.
 
  • #9
abc5 said:
Hello everyone,

I am not sure about this issue and this is the reason why I am asking this question. I can write many sentences on this topic, but I will try to make my point as short is possible.

I will suppose you are familiar with multiverse idea and anthropic principle..

My question is: Let's suppose there are billions and billions of other universes, does that solve problem of fine-tuning? Wouldn't there still have to be some fundamental laws which creates universes in multiverse- in other words, wouldn't there have to be "multiverse generator" which would have to be fine-tuned "for creating other universes with different constants"... Am I missing something, or with multiverse theory problem is not solved, just pushed one step further?
Yes. Multiverse theories typically have a mechanism for the production of a large number of regions like the one we live in. Eternal inflation is one such mechanism that has been proposed.

Also, multiverse theories can only explain fine tuning if that fine tuning is necessary for any observers to exist. That's often not very easy to demonstrate.
 
  • #10
Chalnoth said:
Also, multiverse theories can only explain fine tuning if that fine tuning is necessary for any observers to exist. That's often not very easy to demonstrate.
If there is no fine-tuning necessary there is no need to explain fine-tuning.
 
  • #11
abc5 said:
Hello everyone,

I am not sure about this issue and this is the reason why I am asking this question. I can write many sentences on this topic, but I will try to make my point as short is possible.

I will suppose you are familiar with multiverse idea and anthropic principle..

My question is: Let's suppose there are billions and billions of other universes, does that solve problem of fine-tuning? Wouldn't there still have to be some fundamental laws which creates universes in multiverse- in other words, wouldn't there have to be "multiverse generator" which would have to be fine-tuned "for creating other universes with different constants"... Am I missing something, or with multiverse theory problem is not solved, just pushed one step further?

You are right, the multiverse just pushes the problem one step further. That's what scientists do. It keeps them busy and off of drugs.

More specifically, it obviates fine tuning of physical constants, but it doesn't explain how the whole situation came to be in the first place. But who knows? You've got to take these things one step at a time.
 
  • #12
The multiverse generator might be eternal inflation or the many worlds of Qm, or maybe a cyclic universe with different constants in each cycle. Or maybe one universe with varying constants in it. i don't see why these have to be fine tuned. They may or may not be true.
 
  • #13
The multiverse does one thing very well, it explains observations that appear random or improbable, like the values of physical constants. Under most multiverse theories, all possible values for physical constants, and combinations thereof, are realized somewhere in the multiverse. We just happen to reside in one that has the particular values we measure. This yields a satisfyingly high probability [100%] a universe like ours exists - reducing our reality to an anomalous statistic and disincentivizes scientific inquiry .
 
  • #14
Chronos said:
The multiverse does one thing very well, it explains observations that appear random or improbable, like the values of physical constants. Under most multiverse theories, all possible values for physical constants, and combinations thereof, are realized somewhere in the multiverse. We just happen to reside in one that has the particular values we measure. This yields a satisfyingly high probability [100%] a universe like ours exists - reducing our reality to an anomalous statistic and disincentivizes scientific inquiry .

Sounds pretty boring.
 
  • #15
Chronos said:
The multiverse does one thing very well, it explains observations that appear random or improbable, like the values of physical constants. Under most multiverse theories, all possible values for physical constants, and combinations thereof, are realized somewhere in the multiverse. We just happen to reside in one that has the particular values we measure. This yields a satisfyingly high probability [100%] a universe like ours exists - reducing our reality to an anomalous statistic and disincentivizes scientific inquiry .
Drakkith said:
Sounds pretty boring.
I always say that a theory that can explain anything and everything explains nothing - boring indeed.

Garth
 
  • #16
Garth said:
I always say that a theory that can explain anything and everything explains nothing - boring indeed.

Garth

On the other hand, it seems that we should be open to the possibility that some facts may have no non-boring explanation.
 
  • #17
mfb said:
If there is no fine-tuning necessary there is no need to explain fine-tuning.
It is certainly possible for apparent fine tuning to be explained by as-yet-unknown physical laws creating relationships between different parameters. But there's also no reason to believe such explanations exist if the apparent fine tuning is necessary for any observers to exist.

We may eventually be forced to conclude that there is no explanation for such apparent fine tuning except that the fundamental laws are prolific and certain pieces of apparent fine tuning are necessary for observers.
 
  • #18
stevendaryl said:
On the other hand, it seems that we should be open to the possibility that some facts may have no non-boring explanation.

Indeed the question "why are planetary orbits fine tuned for life" is answered in just such a manner. There is no deeper mechanism at play for selecting Earth like planets in the Goldilocks zone. As best we can tell, it's purely a matter of having large ensembles and the anthropic principle.
 
  • #19
The mulitverse 'expains' everything. It eliminates the need for scientiific inquiry. It is little better than a rartional version of theology, You merely replace your deity of choice with probabilities.
 
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  • #20
Chronos said:
The mulitverse 'expains' everything. It eliminates the need for scientiific inquiry. It is little better than a rartional version of theology, You merely replace your deity of choice with probability.
This is completely false and you should be aware of that fact. Many specific multiverse models have testable predictions. Some are incomplete or poorly constructed and make no predictions, but that shouldn't poison the entire paradigm.

It's really sad that so many dismiss multiverse models out of hand simply because they make them uncomfortable.
 
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  • #21
Chalnoth said:
This is completely false and you should be aware of that fact. Many specific multiverse models have testable predictions. Some are incomplete or poorly constructed and make no predictions, but that shouldn't poison the entire paradigm.
Such as the CMB Cold Spot or The 'Dark' Flow? And yes the evidence has not stood up in the Planck data and so those models have proved to be falsifiable.

However, on the other hand such data could have been just a cosmological non-gaussian distribution of matter.

If hard evidence of other universes should be discovered, such as (being highly speculative) a future gravity wave telescope seeing 'through' the 'singularity' at the heart of a black hole - or the big bang - and image other universes beyond, then the multiverse will enter the realm of hard observed science. Until such time of incontrovertible evidence it remains in the realm of interesting speculation.
t's really sad that so many dismiss multiverse models out of hand simply because they make them uncomfortable.
I'm not uncomfortable with the hypothesis of the multiverse - if God/Nature (using 'God' in the "God does not play dice" sense) made one universe He/She/It can make as many as they want.

I just think it makes bad science.
Steinhardt: My concern was that the multiverse is a ‘theory of anything’, a proposal that allows all possible cosmological outcomes (smooth or not smooth, curved or flat, etc.) and, consequently, is not subject to empirical tests. Some claim that superstring theory allows exponentially many (or perhaps infinitely many) possibilities for the fundamental laws (masses of particles, types of forces, etc.) and that there is no guiding principle to determine which set of physical laws is more probable. The sets of laws comprise what is called the “string landscape.”

Combine the inflationary multiverse with the string landscape, and now one has a ‘supertheory of anything’: both the cosmological properties and the microphysical properties of the universe are accidental and unpredictable.

As we understand superstring theory better, I truly hope we find that there are sound reasons why the physical laws we observe are naturally selected. Superstring theory, combined with an improved cosmological picture, may then lead to a powerfully explanatory and predictive theory.
(Emphasis mine)

Garth
 
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  • #22
Garth said:
I'm not uncomfortable with the hypothesis of the multiverse - if God/Nature (using 'God' in the "God does not play dice sense") made one universe He/She/It can make as many as they want.

I just think it makes bad science. (Emphasis mine)
Just because it's tricky to get right doesn't mean it's bad science. It just means it's tricky to get right.

Especially when you consider that the standard model unambiguously predicts a multiverse (specifically with regards to the Cabibo angle varying from region to region, which impacts the behavior of the weak nuclear force), and so far GUT's predict an even more diverse multiverse.
 
  • #23
Chalnoth said:
Especially when you consider that the standard model unambiguously predicts a multiverse (specifically with regards to the Cabibo angle varying from region to region, which impacts the behavior of the weak nuclear force), and so far GUT's predict an even more diverse multiverse.
In every theory where the parameters, such as the Cabibo angle, have no generally accepted theory that explains why the measured values are what they are, the standard response is to hypothesise that they are determined at some early stage by a stochastic spontaneous symmetry breaking.

By using a stochastic process as a hypothesis the approach has to assume that there is an ensemble of other universes, where in other universes the symmetry breaking process results in different values of the parameter in question.

Such an assumption, that the parameters are simply the outcome of random chance, short circuits any investigation into any possible physical cause, an explicit symmetry breaking, that has determined those particular values and thus tends to dissuade further research for such causes.

The multiverse is therefore an a priori assumption of such an approach, not an unambiguous prediction, and one that may actually prevent further discovery.

Garth
 
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  • #24
Garth said:
In every theory where the parameters, such as the Cabibo angle, have no generally accepted theory that explains why the measured values are what they are, the standard response is to hypothesise that they are determined at some early stage by a stochastic spontaneous symmetry breaking.

By using a stochastic process as a hypothesis the approach has to assume that there is an ensemble of other universes, where in other universes the symmetry breaking process results in different values of the parameter in question.

Such an assumption, that the parameters are simply the outcome of random chance, short circuits any investigation into any possible physical cause, an explicit symmetry breaking, that has determined those particular values and thus tends to dissuade further research for such causes.

The multiverse is therefore an a priori assumption of such an approach, not an unambiguous prediction, and one that may actually prevent further discovery.
Nope. The multiverse is the absence of an assumption. Explicit symmetry breaking requires adding additional assumptions to the theory. With spontaneous symmetry breaking, one need only postulate a higher-order symmetry, such as SO(10). You then tend to get a number of local minima within its interaction potential, some of which have very long lifetimes.

Explicit symmetry breaking requires that you have SO(10) plus an additional rule that determines how the symmetry is broken.

Also, Garth, it is people like yourself that are attempting to dissuade further research. Even if some particular symmetries are broken spontaneously, then there remains the possibility that some other symmetries are broken explicitly. It makes precisely zero sense to discourage any investigation into spontaneous symmetry breaking because you're uncomfortable with the multiverse.
 
  • #25
Chalnoth said:
Nope. The multiverse is the absence of an assumption.
That statement itself is quite an assumption!
It makes precisely zero sense to discourage any investigation into spontaneous symmetry breaking because you're uncomfortable with the multiverse.
As I said, I am very comfortable with the hypothesis of a multiverse - but in order for it to be other than just a hypothesis I waiting for you to show me one of these other universes.

Garth
 
  • #26
Garth said:
That statement itself is quite an assumption!As I said, I am very comfortable with the hypothesis of a multiverse - but in order for it to be other than just a hypothesis I waiting for you to show me one of these other universes.

Garth
I can't show the inside of a black hole either or Hawking radiation, so do you assume there is no inside of black hole and no such things as Hawking radiation?
 
  • #27
palmer eldtrich said:
I can't show the inside of a black hole either or Hawking radiation, so do you assume there is no inside of black hole and no such things as Hawking radiation?
Of course not.

There is plenty of evidence that BH's themselves exist (Cygnus X-1, M87 etc.) with their appropriate event horizons and therefore it is a reasonable assumption that those horizons have interiors.

As to what happens in those interiors we are reliant on the theoretical extrapolation of the well tested theory of GR. But in doing so we are extending the theory well beyond the lower curvature regimes in which the theory has been tested and so have to be wary. A quantum-gravity theory modification of GR might predict a different interior.

It will be interesting to see what such a Q-G theory will say about Hawking radiation, which to date has not been observed.

Remember
“I would rather have questions that can't be answered than answers that can't be questioned.”― Richard Feynman
[PLAIN]http://www.goodreads.com/author/show/1429989.Richard_Feynman[/PLAIN]

Garth
 
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  • #28
The only observational evidence you have for black holes is their external influence on their surroudings. You have no evidence they have an interior. You agree that Hawking radiation has not been observed. So why shouldn't we say that the idea that black holes have interiors or emit Hawking radiation is Sci Fi fantasy or theology or whatever other derogatory term you want to throw.
Clearly there is a difference between believing in black hole interiors and Hawking radiation and theology. The former is well motivated by physics we understand, the latter isn't. in other words we can have some trust in the predictions of a theory beyond what we can observe if we can confirm its predictions for things we can observe. That trust won't be as high as the things we observe but it would not be zero either.
In the case of the multiverse , it is not a hypothesis but a prediction of inflation; sort of .
The evidence for inflation is not zero but its not as good as black holes. The theoretical motivation is that according to Guth and Steinhardt, eternal inflation is a generic property of inflation. Its possible inflation didnt happen, also that we have misunderstood inflation and its not really eternal. But at the moment i would say it looks like from the current evidence and theorertical understanding we have that inflation did happen and it is eternal.
I think the problem is that people think science should give us clear answers , but why should it? Maybe the universe isn't that kind. I think the reality is that confidence in statements should a spectrum, not a black and white answer. Sometimes our confidence enables us to make statements with no reasonable doubt , other times there are plenty of doubts but that's not the same as believing in theology or fantasy. Other times belief is just fantasy. i think the multiverse is somewhere along this spectrum. it is not a confirmed fact but to call it fantasy or theology is just silly .
 
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  • #29
palmer eldtrich said:
Other times belief is just fantasy. i think the multiverse is somewehre along this spectrum. it is not a confirmed fact but to call it fantasy or theology is just silly .
I agree - except that I never called it "fantasy or theology" - the word I used was 'hypothesis'.

But I do also agree with Steinhardt about Inflation and the multiverse it begets:
Since 1983, it has become clear that inflation is very flexible (parameters can be adjusted to give any result) and generically leads to a multiverse consisting of patches in which any outcome is possible. Imagine a scientific theory that was designed to explain and predict but ends up allowing literally any conceivable possibility without any rule about what is more likely. What good is it? It rules out nothing and can never be put to a real test.

Garth
 
  • #30
I understand you didnt call it fantasy or theology but many people have, including on this forum. I am glad we agree that our confidence in ideas ranges along a spectrum and that the multiverse is neither confirmed scientific fact nor unfounded fantasy. Steinhardt I think contradicts himself because he says you can discriminate between his ekpyrotic model and inflation by observing the gravitational wave spectrum. but if that's true then how does he justify that inflation can't be tested?
Maybe you can make models of inflation that didnt have Omega =1 and ns =.96 etc but I am not convinced they would be taken them so seriously. The fact is inflation is the best model we have right now for structure formation. Maybe a better model like Ekpyrosis will replace it one day, but so far that hasnt happened. As we understand inflaiton at the moment it looks like it generates a mulitverse. So i think we have good scientific reasons to believe in a multiverse. But clearly that belief should not be at the same level that we believe in black holes. The whole argument is based on a false notion that science should give us definitive answers to questions. I wish the world worked that way, but alas it doesnt.
 
  • #31
palmer eldtrich said:
Steinhardt I think contradicts himself because he says you can discriminate between his ekpyrotic model and inflation by observing the gravitational wave spectrum. but if that's true then how does he justify that inflation can't be tested?
The Ekpyrotic universe model predicts no primordial gravitational waves detectable by BICEP2, whereas Inflation in many guises did. If such g-w's had been found that would have falsified Steinhardt's model.

In fact they weren't discovered as we know, BICEP2 picked up a signal from dust and whether there is a weaker g-w signal hidden in there has yet to be determined.

So it might seem that the Ekpyrotic model has won over the Inflationary one, however Inflation is so flexible that one can simply constrain the parameters fed into the theory and produce a weaker or zero prediction of the g-w signal and thus save the theory. Actually we all do this with our theories - it's just that inflation is more flexible than most.
So i think we have good scientific reasons to believe in a multiverse. But clearly that belief should not be at the same level that we believe in black holes. The whole argument is based on a false notion that science should give us definitive answers to questions. I wish the world worked that way, but alas it doesnt.
Indeed, especially when we are scratching away at the boundaries of what is observable.

Garth
 
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  • #32
Garth said:
That statement itself is quite an assumption!
Why do you think this?

If you take the standard model at face-value using the minimal assumptions required to explain the available evidence, then you have a model which unambiguously predicts a multiverse. You can, of course, add assumptions to get rid of the multiverse, but then you're just making unwarranted assumptions without evidence to support them. Maybe you can get rid of the multiverse (in this case, different low-energy physical laws in different locations), but I find that prospect highly unlikely.

Fine tuning that is required for any observers to exist is in itself powerful evidence of fine tuning. The picture here is that if we imagine the full possible configuration space of the universe as given by our current state of knowledge as a sheet of paper, and we then draw a dot to represent the part of that configuration space where life is possible. Those that want to get rid of the multiverse tend to argue that the rest of the paper isn't real: it's just an illusion due to our lack of knowledge, and the real space of possibilities aren't much larger than that small dot.

But the question that I ask is: why should that be the case? Why should the total space of possibilities tailor itself perfectly for life to exist?

I think most theorists expect that a significant fraction of that space of possibilities is impossible, and that knowledge of the correct GUT will demonstrate this. But I don't think there's any reasonable argument to be had that it won't remain much, much larger than the part of the space where life is possible. The cosmological constant is good example here: independent of our current observations, it is impossible for any structure formation if the magnitude of the cosmological constant were more than about ##10^{-120}## in natural units. For a long time, most theorists believed that there must, therefore, be some kind of symmetry that sets the cosmological constant to zero. But that has proven very difficult (for discussion, Sean Carroll described some of the difficulties in his book here).

Granted, the fact that it's hard to write down theories which predict a small or zero cosmological constant doesn't necessarily mean that it can't be true. But there's just no reason to prefer a unique universe as a default assumption. The simplest assumptions, given current knowledge, lead to some kind of multiverse.
 
  • #33
Garth said:
The Ekpyrotic universe model predicts no primordial gravitational waves detectable by BICEP2, whereas Inflation in many guises did. If such g-w's had been found that would have falsified Steinhardt's model.

In fact they weren't discovered as we know, BICEP2 picked up a signal from dust and whether there is a weaker g-w signal hidden in there has yet to be determined.

So it might seem that the Ekpyrotic model has won over the Inflationary one, however Inflation is so flexible that one can simply constrain the parameters fed into the theory and produce a weaker or zero prediction of the g-w signal and thus save the theory. Actually we all do this with our theories - it's just that inflation is more flexible than most.Indeed, especially when we are scratching away at the boundaries of what is observable.

Garth
That's like saying Mars rovers have shown theories that life is unique on Earth have won over theories that imply life in the universe is not unique to Earth. Technically true but hardly impressive. It's hard to find life outside of Earth even if its there. Its hard to find gravity waves even if they are there. I spoke to a number of people that worked on Planck and they said they had very little expectation of finding the b mode ( although they hoped they might get lucky ) so not finding it was not really a big shock and I don't think you should read too much into it.
 
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  • #34
The multiverse hypothesis is filled with paradoxes, as deep and varied as the number of metastable vacuum states.
 
  • #35
Under a multiverse scenario, such as that proposed by Tegmark, you cannot forbid causal connections between different 'universes'. So there must surely be other universes that are observationally accessible to us. So, to quote Fermi, where are they?
 

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